Colour-colour-diagrams (CCDs) given in rows 1–3, as well as a Gaia-2MASS diagram (see text for details). All three columns show the same model data, but colour-coded by different properties: carbon excess (input parameter; left column), resulting grain size (middle), and amount of dust (condensation degree times C – O abundance; right). Model symbols in light blue indicate models with no wind. Observations are plotted as grey symbols in the CCDs (top three rows), drawn from Jones et al. (2017).